1. Field of the Invention
The invention relates to a heat curing reaction resin mixture for impregnating the insulation of electrical equipment formed of insulating sleeves which are made of materials in sheet or tape form having a heat resistance which corresponds to at least Class H of electrical conductors, particularly of winding bars or coils of electric machines, and for the manufacture of molded material with or without inserts. More particularly, the invention relates to a heat curing reaction resin mixture comprising, preferably, purified polyisocyanate and polyepoxy resin compounds which contain an accelerator system (catalyst).
2. Description of the Prior Art
Such a heat curing reaction resin mixture for impregnating the windings of electric machines is described in German Offenlegungsschrift No. 24 44 458. With this type of polyisocyanate epoxy resin mixture, molded materials of high dimensional heat resistance, high thermal fatigue strength, as well as with good mechanical and electrical properties can be produced by cross-linking, in the presence of certain accelerator systems. Use of this mixture in engineering applications has, however, encountered difficulties, as the known accelerators or accelerator systems which are mentioned in the German Offenlegungsschrift No. 24 44 458, cause the mixture to harden either too fast or too slow. As a result, with such mixture it becomes impossible, for example, to produce insulation economically, as the viscosity of the mixture either increases too fast, in the case of the fast accelerator systems and, thus, no longer ensures complete impregnation, or increases too slowly, in the case of the slow accelerator systems, and thus, prevents hardening within an economically justifiable time.
It is, therefore, an object of the present invention to develop a heat curing reaction resin mixture of the above type whose viscosity does not appreciably change at room temperature, but which nevertheless can be hardened at higher temperatures in economically short times.